Methods and systems for fuel ethanol content determination via an oxygen sensor

ABSTRACT

Methods are provided for accurately learning part-to-part variability of an intake or exhaust oxygen sensor. A correction factor is learned based on sensor readings at voltages above and below a voltage corresponding to dry air conditions. An ethanol transfer function is then adjusted based on the learned correction factor so as to improve the accuracy of combusted fuel ethanol content estimation.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 14/151,574, “METHODS AND SYSTEMS FOR FUEL ETHANOLCONTENT DETERMINATION VIA AN OXYGEN SENSOR,” filed on Jan. 9, 2014, theentire contents of which are hereby incorporated by reference for allpurposes.

BACKGROUND AND SUMMARY

Intake and/or exhaust gas sensors may be operated to provide indicationsof various exhaust gas constituents. For example, US 20120037134describes detecting engine intake dilution using an intake gas oxygensensor. In alternate approaches, engine dilution may be estimated by anexhaust gas oxygen sensor. The estimated engine dilution may be used toadjust various engine operating parameters, such as fueling and air-fuelratio. As another example, U.S. Pat. No. 5,145,566 describes detectingwater content in the exhaust gas using an exhaust gas oxygen sensor. Inalternate approaches, water content in exhaust gas recirculated to theengine intake (EGR) may be estimated using an intake gas oxygen sensor.Water content estimated using an intake or exhaust gas oxygen sensor maybe used to infer an ambient humidity during engine operation. Furtherstill, the water content may be used to infer an alcohol content of afuel burned in the engine.

However, the inventors have recognized that oxygen sensors (both intakeand exhaust oxygen sensors) can have significant part-to-partvariability. For example, without any compensation, the variability inoxygen measurement by the sensor can be in the range of 15%. Thisvariability in the sensor output can lead to a substantial error in themeasurement of fuel alcohol content and engine dilution. For example,based on the variability of the sensor, an alcohol transfer function(used to estimate fuel alcohol content based on the oxygen sensoroutput) may vary. If a known transfer function for a nominal sensor isused, the fuel alcohol content may be overestimated or underestimated.As such, to correctly measure the fuel alcohol content, the oxygensensor output needs to be compensated for this part-to-part variabilitywhich is affected not only by the age of the sensor, but also ambientconditions (in particular, ambient humidity levels), as well as thepresence of additional diluents (such as purge or crankcase ventilationvapors).

The above issues may be addressed and accuracy of fuel alcohol contentestimation by an (intake or exhaust) oxygen sensor can be improved by amethod that better compensates for sensor part-to-part variability. Oneexample method comprises, during selected conditions, operating anoxygen sensor at a lower reference voltage where water molecules are notdissociated to generate a first output and at a higher reference voltagewhere water molecules are fully dissociated to generate a second output.The method further comprises learning a correction factor for the sensorbased on the first and second output. The method may further compriseadjusting a parameter based on an alcohol content, the alcohol contentof fuel combusted in the engine estimated based on each of the firstoutput and the learned correction factor for the sensor. In this way,oxygen sensor reliability is improved.

In one example, during selected conditions, the oxygen sensor isoperated to determine an oxygen sensor reading corrected for dry airconditions. For example, during conditions when purge and crankcaseventilation gases are not ingested in an engine intake manifold, thereference voltage of an intake oxygen sensor may be modulated.Alternatively, in embodiments where the oxygen sensor is an exhaustoxygen sensor, the selected conditions may include engine non-fuelingconditions, such as a deceleration fuel shut-off (DFSO) event.Specifically, the reference voltage of the oxygen sensor may be raisedfrom a first, lower voltage where the output (e.g., pumping current) isrepresentative of an oxygen reading in humid conditions, to a second,higher voltage where the output (e.g., pumping current) isrepresentative of an increase in oxygen due to the full dissociation ofhumid. A dry air pumping current may then be determined based on a ratiobetween the first output and the second output, the dry air pumpingcurrent indicative of an oxygen reading in dry air. The dry air oxygenreading (the ratio between the first and second output) is then used todetermine an alcohol transfer function correction. The correctedtransfer function and the humid air oxygen reading (first output) maythen be used to estimate a fuel alcohol content. The estimated fuelalcohol content can then be used to estimate an engine operatingparameter, such as a desired air-fuel ratio for combustion. As anexample, the controller may adjust an air-fuel ratio correction based onthe estimated fuel alcohol content.

In this way, the part-to-part variability of an intake or exhaust oxygensensor may be better learned, including part-to-part variability due tosensor aging. By learning the variability, the need for a compensationresistor configured to compensate for the part-to-part variability isreduced, providing cost and component reduction benefits. By using a dryair oxygen estimate provided by the oxygen sensor to correct an alcoholtransfer function, irregularities in fuel ethanol estimation may bereduced. Overall, reliability of the sensor output is increased.Further, accuracy of fuel alcohol estimated based on oxygen sensoroutput is also increased. Since the sensor output and fuel alcoholestimate are used to adjust various engine operating parameters, overallengine performance is improved.

It will be understood that the summary above is provided to introduce insimplified form a selection of concepts that are further described inthe detailed description, which follows. It is not meant to identify keyor essential features of the claimed subject matter, the scope of whichis defined by the claims that follow the detailed description. Further,the claimed subject matter is not limited to implementations that solveany disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine including an exhaust gasoxygen sensor and an intake gas oxygen sensor.

FIG. 2 shows a schematic diagram of an example oxygen sensor.

FIG. 3 shows a flow chart illustrating a routine for accuratelyestimating an amount of alcohol in fuel, while correcting an alcoholtransfer function for effects of oxygen sensor part-to-part variation.

FIG. 4 shows a graph depicting oxygen sensor output under varioushumidity conditions with respect to applied voltage.

FIG. 5 shows a graph depicting impact of oxygen sensor part-to-partvariability on fuel ethanol estimation.

FIG. 6 shows a flow chart illustrating a routine for controlling anengine based on the output of an intake or exhaust gas oxygen sensor.

DETAILED DESCRIPTION

The following description relates to a method for determining an amountof alcohol in a fuel mixture (e.g., ethanol and gasoline) based onoutputs from an intake air or exhaust gas sensor, such as an oxygensensor. For example, the sensor may be operated a first, lower voltageto obtain a first output which indicates a humid air oxygen reading. Thesensor may then be operated at a second, higher voltage to obtain asecond output which indicates a humid air oxygen reading wherein all thehumidity in the air has dissociated at the oxygen sensor. A middlevoltage between the first, lower voltage and the second, higher voltagemay produce an oxygen sensor output indicative of a dry air oxygenreading wherein partial dissociation of the humidity occurs. A dry airoxygen reading may then be estimated by a ratio between the first outputand the second output. An alcohol transfer function may be correctedbased on the estimated dry air oxygen reading and the first output maythen be corrected based on the corrected alcohol transfer function toinfer an amount of alcohol in fuel injected to the engine. In thismanner, part-to-part variability of different oxygen sensors may bereduced such that a more accurate indication of fuel alcohol content maybe determined. In one example, engine operating parameters such as sparktiming and/or fuel injection amount may be adjusted based on thedetected amount of alcohol in the fuel. In this manner, engineperformance, fuel economy, and/or emissions may be maintained orimproved despite the varying amounts of alcohol in the fuel.

Referring now to FIG. 1, a schematic diagram showing one cylinder of amulti-cylinder engine 10, which may be included in a propulsion systemof an automobile, is illustrated. The engine 10 may be controlled atleast partially by a control system including a controller 12 and byinput from a vehicle operator 132 via an input device 130. In thisexample, the input device 130 includes an accelerator pedal and a pedalposition sensor 134 for generating a proportional pedal position signalPP. A combustion chamber (i.e., cylinder) 30 of the engine 10 mayinclude combustion chamber walls 32 with a piston 36 positioned therein.The piston 36 may be coupled to a crankshaft 40 so that reciprocatingmotion of the piston is translated into rotational motion of thecrankshaft. The crankshaft 40 may be coupled to at least one drive wheelof a vehicle via an intermediate transmission system. Further, a startermotor may be coupled to the crankshaft 40 via a flywheel to enable astarting operation of the engine 10.

The combustion chamber 30 may receive intake air from an intake manifold44 via an intake passage 42 and may exhaust combustion gases via anexhaust passage 48. The intake manifold 44 and exhaust passage 48 canselectively communicate with the combustion chamber 30 via respectiveintake valve 52 and exhaust valve 54. In some embodiments, thecombustion chamber 30 may include two or more intake valves and/or twoor more exhaust valves.

In this example, the intake valve 52 and exhaust valve 54 may becontrolled by cam actuation via respective cam actuation systems 51 and53. The cam actuation systems 51 and 53 may each include one or morecams and may utilize one or more of cam profile switching (CPS),variable cam timing (VCT), variable valve timing (VVT), and/or variablevalve lift (VVL) systems that may be operated by a controller 12 to varyvalve operation. The position of the intake valve 52 and exhaust valve54 may be determined by position sensors 55 and 57, respectively. Inalternative embodiments, the intake valve 52 and/or exhaust valve 54 maybe controlled by electric valve actuation. For example, the cylinder 30may alternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT systems.

In some embodiments, each cylinder of the engine 10 may be configuredwith one or more fuel injectors for providing fuel thereto. As anon-limiting example, the cylinder 30 is shown including one fuelinjector 66. The fuel injector 66 is shown coupled directly to thecylinder 30 for injecting fuel directly therein in proportion to thepulse width of signal FPW received from the controller 12 via anelectronic driver 68. In this manner, the fuel injector 66 provides whatis known as direct injection (hereafter also referred to as “DI”) offuel into the combustion cylinder 30.

It will be appreciated that in an alternate embodiment, the injector 66may be a port injector providing fuel into the intake port upstream ofthe cylinder 30. It will also be appreciated that the cylinder 30 mayreceive fuel from a plurality of injectors, such as a plurality of portinjectors, a plurality of direct injectors, or a combination thereof.

A fuel tank in a fuel system 172 may hold fuels with different fuelqualities, such as different fuel compositions. These differences mayinclude different alcohol content, different octane, different heats ofvaporization, different fuel blends, and/or combinations thereof etc.The engine may use an alcohol containing fuel blend such as E85 (whichis approximately 85% ethanol and 15% gasoline) or M85 (which isapproximately 85% methanol and 15% gasoline). Alternatively, the enginemay operate with other ratios of gasoline and ethanol stored in thetank, including 100% gasoline and 100% ethanol, and variable ratiostherebetween, depending on the alcohol content of fuel supplied by theoperator to the tank. Moreover, fuel characteristics of the fuel tankmay vary frequently. In one example, a driver may refill the fuel tankwith E85 one day, and E10 the next, and E50 the next. As such, based onthe level and composition of the fuel remaining in the tank at the timeof refilling, the fuel tank composition may change dynamically.

The day to day variations in tank refilling can thus result infrequently varying fuel composition of the fuel in the fuel system 172,thereby affecting the fuel composition and/or fuel quality delivered bythe injector 66. The different fuel compositions injected by theinjector 66 may herein be referred to as a fuel type. In one example,the different fuel compositions may be qualitatively described by theirresearch octane number (RON) rating, alcohol percentage, ethanolpercentage, etc.

It will be appreciated that while in one embodiment, the engine may beoperated by injecting the variable fuel blend via a direct injector, inalternate embodiments, the engine may be operated by using two injectorsand varying a relative amount of injection from each injector. It willbe further appreciated that when operating the engine with a boost froma boosting device such as a turbocharger or supercharger (not shown),the boosting limit may be increased as an alcohol content of thevariable fuel blend is increased.

Continuing with FIG. 1, the intake passage 42 may include a throttle 62having a throttle plate 64. In this particular example, the position ofthe throttle plate 64 may be varied by the controller 12 via a signalprovided to an electric motor or actuator included with the throttle 62,a configuration that is commonly referred to as electronic throttlecontrol (ETC). In this manner, the throttle 62 may be operated to varythe intake air provided to the combustion chamber 30 among other enginecylinders. The position of the throttle plate 64 may be provided to thecontroller 12 by a throttle position signal TP. The intake passage 42may include a mass air flow sensor 120 and a manifold air pressuresensor 122 for providing respective signals MAF and MAP to controller12.

An ignition system 88 can provide an ignition spark to the combustionchamber 30 via a spark plug 92 in response to a spark advance signal SAfrom the controller 12, under select operating modes. Though sparkignition components are shown, in some embodiments, the combustionchamber 30 or one or more other combustion chambers of the engine 10 maybe operated in a compression ignition mode, with or without an ignitionspark.

An exhaust gas sensor 126 is shown coupled to the exhaust passage 48upstream of an emission control device 70. The sensor 126 may be anysuitable sensor for providing an indication of exhaust gas air/fuelratio such as a linear oxygen sensor or UEGO (universal or wide-rangeexhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heatedEGO), a NO_(x), HC, or CO sensor. The emission control device 70 isshown arranged along the exhaust passage 48 downstream of the exhaustgas sensor 126. The device 70 may be a three way catalyst (TWC), NO_(x)trap, various other emission control devices, or combinations thereof.In some embodiments, during operation of engine 10, emission controldevice 70 may be periodically reset by operating at least one cylinderof the engine within a particular air/fuel ratio.

As shown in the example of FIG. 1, the system further includes an intakeair sensor 127 coupled to the intake passage 44. The sensor 127 may beany suitable sensor for providing an indication of exhaust gas air/fuelratio such as a linear oxygen sensor or UEGO (universal or wide-rangeexhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heatedEGO), a NO_(x), HC, or CO sensor.

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from the exhaustpassage 48 to the intake passage 44 via an EGR passage 140. The amountof EGR provided to the intake passage 44 may be varied by the controller12 via an EGR valve 142. Further, an EGR sensor 144 may be arrangedwithin the EGR passage 140 and may provide an indication of one or moreof pressure, temperature, and concentration of the exhaust gas. Undersome conditions, the EGR system may be used to regulate the temperatureof the air and fuel mixture within the combustion chamber, thusproviding a method of controlling the timing of ignition during somecombustion modes. Further, during some conditions, a portion ofcombustion gases may be retained or trapped in the combustion chamber bycontrolling exhaust valve timing, such as by controlling a variablevalve timing mechanism.

The controller 12 is shown in FIG. 1 as a microcomputer, including amicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. The controller 12 may receivevarious signals from sensors coupled to the engine 10, in addition tothose signals previously discussed, including measurement of inductedmass air flow (MAF) from the mass air flow sensor 120; engine coolanttemperature (ECT) from a temperature sensor 112 coupled to a coolingsleeve 114; a profile ignition pickup signal (PIP) from a Hall effectsensor 118 (or other type) coupled to the crankshaft 40; throttleposition (TP) from a throttle position sensor; and absolute manifoldpressure signal, MAP, from the sensor 122. Engine speed signal, RPM, maybe generated by the controller 12 from signal PIP.

The storage medium read-only memory 106 can be programmed with computerreadable data representing instructions executable by the processor 102for performing the methods described below as well as other variantsthat are anticipated but not specifically listed.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Next, FIG. 2 shows a schematic view of an example embodiment of anoxygen sensor 200 configured to measure a concentration of oxygen (O₂)in an intake airflow in an intake passage or an exhaust gas stream in anexhaust passage. The sensor 200 may operate as UEGO sensor 126 of FIG.1, for example. The sensor 200 comprises a plurality of layers of one ormore ceramic materials arranged in a stacked configuration. In theembodiment of FIG. 2, five ceramic layers are depicted as layers 201,202, 203, 204, and 205. These layers include one or more layers of asolid electrolyte capable of conducting ionic oxygen. Examples ofsuitable solid electrolytes include, but are not limited to, zirconiumoxide-based materials. Further, in some embodiments, a heater 207 may bedisposed in thermal communication with the layers to increase the ionicconductivity of the layers. While the depicted oxygen sensor is formedfrom five ceramic layers, it will be appreciated that the oxygen sensormay include other suitable numbers of ceramic layers.

The layer 202 includes a material or materials creating a diffusion path210. The diffusion path 210 is configured to introduce exhaust gasesinto a first internal cavity 222 via diffusion. The diffusion path 210may be configured to allow one or more components of intake air orexhaust gases, including but not limited to a desired analyte (e.g.,O₂), to diffuse into internal cavity 222 at a more limiting rate thanthe analyte can be pumped in or out by a pumping electrodes pair 212 and214. In this manner, a stoichiometric level of O₂ may be obtained in thefirst internal cavity 222.

The sensor 200 further includes a second internal cavity 224 within thelayer 204 separated from the first internal cavity 222 by the layer 203.The second internal cavity 224 is configured to maintain a constantoxygen partial pressure equivalent to a stoichiometric condition, e.g.,an oxygen level present in the second internal cavity 224 is equal tothat which the intake air or exhaust gas would have if the air-fuelratio was stoichiometric. The oxygen concentration in the secondinternal cavity 224 is held constant by pumping voltage V_(cp). Herein,the second internal cavity 224 may be referred to as a reference cell.

A pair of sensing electrodes 216 and 218 is disposed in communicationwith the first internal cavity 222 and the reference cell 224. Thesensing electrodes pair 216 and 218 detects a concentration gradientthat may develop between the first internal cavity 222 and the referencecell 224 due to an oxygen concentration in the intake air or exhaust gasthat is higher than or lower than the stoichiometric level. A highoxygen concentration may be caused by a lean intake air or exhaust gasmixture, while a low oxygen concentration may be caused by a richmixture.

A pair of pumping electrodes 212 and 214 is disposed in communicationwith the internal cavity 222, and is configured to electrochemicallypump a selected gas constituent (e.g., O₂) from internal cavity 222through layer 201 and out of the sensor 200. Alternatively, the pair ofpumping electrodes 212 and 214 may be configured to electrochemicallypump a selected gas through layer 201 and into internal cavity 222.Herein, the pumping electrodes pair 212 and 214 may be referred to as anO₂ pumping cell.

The electrodes 212, 214, 216, and 218 may be made of various suitablematerials. In some embodiments, the electrodes 212, 214, 216, and 218may be at least partially made of a material that catalyzes thedissociation of molecular oxygen. Examples of such materials include,but are not limited to, electrodes containing platinum and/or silver.

The process of electrochemically pumping the oxygen out of or into theinternal cavity 222 includes applying a voltage V_(p) across the pumpingelectrode pair 212 and 214. The pumping voltage V_(p) applied to the O₂pumping cell pumps oxygen into or out of the first internal cavity 222in order to maintain a stoichiometric level of oxygen in the cavitypumping cell. The resulting pumping current I_(p) is proportional to theconcentration of oxygen in the exhaust gas. A control system (not shownin FIG. 2) generates the pumping current signal I_(p) as a function ofthe intensity of the applied pumping voltage V_(p) required to maintaina stoichiometric level within the first internal cavity 222. Thus, alean mixture will cause oxygen to be pumped out of the internal cavity222 and a rich mixture will cause oxygen to be pumped into the internalcavity 222.

It should be appreciated that the oxygen sensor described herein ismerely an example embodiment of an oxygen sensor, and that otherembodiments of oxygen sensors may have additional and/or alternativefeatures and/or designs.

As elaborated below, the oxygen sensor of FIG. 2 can be advantageouslyused to estimate an accurate amount of alcohol in the fuel burned in theengine despite part-to-part variability of the intake or exhaust oxygensensor. In particular, by determining an estimated dry air oxygenreading based on a ratio between an oxygen sensor output at a first,lower voltage and an oxygen sensor output at a second, higher voltage,an alcohol transfer function correction may be determined. The correctedtransfer function may then be applied to a humid air oxygen readingdetermined at the first, lower voltage to estimate a fuel alcoholcontent.

Continuing to FIG. 3, a flow chart illustrating a routine 300 foraccurately estimating an amount of alcohol in fuel, while correcting analcohol transfer function for effects of part-to-part variation of anoxygen sensor, such as the oxygen sensor 200 described above withreference to FIG. 2, is shown. Specifically, the routine 300 determinesan amount of alcohol in the fuel injected to the engine, and thus thefuel type, based on voltages applied to a pumping cell of the sensorduring selected engine fueling conditions and further based on analcohol transfer function correction.

At 310 of routine 300, engine operating conditions are determined.Engine operating conditions may include but are not limited to air-fuelratio, amount of EGR entering the combustion chambers, and fuelingconditions, for example.

Once the engine operating conditions are determined, routine 300continues to 312 where it is determined if selected conditions are met.For example, when the oxygen is an intake oxygen sensor positioned inthe intake passage, the selected conditions may include EGR beingenabled and no purge or crankcase ventilation gases being received inthe intake manifold. As another example, when the oxygen sensor is anexhaust gas oxygen sensor positioned in the exhaust passage, theselected conditions may include engine non-fueling conditions.Non-fueling conditions include vehicle deceleration conditions andengine operating conditions in which the fuel supply is interrupted butthe engine continues spinning and at least one intake valve and oneexhaust valve are operating; thus, air is flowing through one or more ofthe cylinders, but fuel is not injected in the cylinders. Undernon-fueling conditions, combustion is not carried out and ambient airmay move through the cylinder from the intake to the exhaust. In thisway, a sensor, such as an intake or exhaust oxygen sensor, may receiveambient air on which measurements, such as ambient humidity detection,may be performed.

As noted, non-fueling conditions may include, for example, decelerationfuel shut-off (DFSO). DFSO is responsive to the operator pedal (e.g., inresponse to a driver tip-out and where the vehicle accelerates greaterthan a threshold amount). DSFO conditions may occur repeatedly during adrive cycle, and, thus, numerous indications of the ambient humidity maybe generated throughout the drive cycle, such as during each DFSO event.As such, the fuel type may be identified accurately based on an amountof water in the exhaust gas despite fluctuations in humidity betweendrive cycles or even during the same drive cycle.

Continuing with FIG. 3, if it is determined that the selected operatingconditions are not met, the routine 300 continues to 313 to continuecurrent oxygen sensor operation (at the current pumping voltage) anddetermine the amount of alcohol in the fuel based on a previouslydetermined correction factor. Conversely, if is determined that selectedoperating conditions are met, routine 300 continues to 314 where a firstpumping voltage (V₁) is applied to the oxygen pumping cell of theexhaust gas sensor and a first pumping current (I_(p1)) is received. Thefirst pumping voltage may have a value such that oxygen is pumped fromthe cell, but low enough that oxygen compounds such as H₂O (e.g., water)are not dissociated (e.g., V₁=450 mV). For example, at the first pumpingvoltage, the oxygen sensor may not dissociate any water molecules.Application of the first voltage generates an output of the sensor inthe form of the first pumping current (I_(p1)) that is indicative of theamount of oxygen in the sample gas. In this example, because the engineis under selected conditions (such as non-fueling conditions), theamount of oxygen may correspond to the amount of oxygen in the fresh airsurrounding the vehicle, or a humid air oxygen reading.

Once the amount of oxygen is determined, routine 300 proceeds to 316where a second pumping voltage (V₂) is applied to the oxygen pumpingcell of the sensor and a second pumping (I_(p2)) current is received.The second voltage may be greater than the first voltage applied to thesensor. In particular, the second voltage may have a value high enoughto dissociate a desired oxygen compound. For example, the second voltagemay be high enough to dissociate all H₂O molecules into hydrogen andoxygen (e.g., V₂=1.1 V). Application of the second voltage generates thesecond pumping current (I₂) that is indicative of the amount of oxygenand water in the sample gas. It will be understood that the term “water”in the “amount of oxygen and water” as used herein refers to the amountof oxygen from the dissociated H₂O molecules in the sample gas.

In one particular example, the second voltage may be 1080 mV, at whichthe water in the air is fully (e.g., completely) dissociated (e.g., 100%of the water in the air is dissociated at 1080 mV). This second voltagemay be larger than a third, middle voltage where water in the air ispartially dissociated (e.g., approximately 40% of the water in the airis dissociated). In one example, the third, middle voltage may be about920 mV. In another example, the third, middle voltage may be about 950mV. As an example, a graph 400 of FIG. 4 shows oxygen sensor output overa range of humidity conditions (e.g., from 1.5% humidity to 4%humidity). As shown, the sensor output at 920 mV corresponds to a dryair reading under the range of humidity conditions. The sensor output at1.1 V corresponds to a humid air reading where all the water in the airhas been dissociated at the sensor and the sensor output at 4.5 Vcorresponds to a humid air reading where no water in the air has beendissociated. Thus, a dry air oxygen reading may be obtained by a ratioof oxygen sensor outputs when the oxygen sensor is operated at 4.5 V and1.1V. In an alternate embodiment, the dry air oxygen reading may beobtained by a ratio of oxygen sensor output when the oxygen sensor isoperated at a voltage below 0.92 V where water is not dissociated (e.g.,not even partially dissociated) and a voltage above 0.92 V where wateris fully dissociated (e.g., 100% dissociated).

At 318, the dry air oxygen reading and related correction factor aredetermined based on the first pumping current and the second pumpingcurrent. For example, as described above, by operating the sensor at 450mV (or a similar voltage where no water is dissociated at the sensor), alower pumping current and oxygen reading may be obtained and byoperating the sensor at 1080 mV (or a similar voltage where all water isdissociated at the sensor) a higher pumping current and oxygen readingmay be obtained. A dry air pumping current indicative of a dry airoxygen reading may then be estimated from a ratio between the lowerpumping current and the higher pumping current. For example, a sum of40% of the higher pumping current and 60% of the lower pumping currentmay be substantially equal to the dry air pumping current and oxygenreading. In an alternate example, different percentages of the higherand lower pumping current may be added together to determine the dry airpumping current. For example, if the higher or lower voltage differ from450 mV and 1080 mV, respectively, the corresponding percentages used todetermine the ratio between the higher and lower pumping currents maydiffer proportionally.

The estimated dry air oxygen reading based on the ratio between thehigher and lower pumping currents (e.g., higher and lower oxygen sensoroutputs corresponding to the higher and lower voltages) may then be usedto determine the correction factor, or alcohol transfer functioncorrection. As described above, the correction factor is a factor thatcompensates for part-to-part variability of the sensor. In one example,the correction factor may be determined based on a ratio of a referencesensor output relative to the estimated dry air oxygen reading at theratio between the first and second voltage. Said another way, thecorrection factor may be determined based on a ratio of the referencesensor output relative to a ratio of the first and second outputs of thesensor generated by applying the first and second voltages,respectively. Once the correction factor is determined, the alcoholtransfer function is updated based on the determined correction factorat 320.

Once the first and second pumping currents are generated, an amount ofwater in the sample gas may be determined at 322 of routine 300 in FIG.3. For example, when the second pumping current is high enough todissociate substantially all water molecules in the sample gas, thefirst pumping current may be subtracted from the second pumping currentto determine a value that corresponds to an amount of water.

Finally, the amount of alcohol in the fuel, and thus the fuel type, maybe identified at 324. For example, the corrected transfer function maybe applied to the first pumping current such that an accurate indicationof an amount of alcohol (e.g., a percent of ethanol) in the fuelinjected to the engine is determined. In some embodiments, the computerreadable storage medium of the control system receiving communicationfrom the sensor may include instructions for identifying the amount ofalcohol.

Thus, based on sensor outputs (e.g., pumping currents) generatedresponsive to voltages applied to the oxygen pumping cell of the intakeair or exhaust gas sensor during engine fueling and non-fuelingconditions and the transfer function correction factor, an accurateindication of the amount alcohol (e.g., percent ethanol) in the fuel maybe identified. Further, once the fuel type is determined, various engineoperating parameters may be adjusted to maintain engine and/or emissionsefficiency, as will be described in detail below.

Method 300 may further include, after 318, determining a correctionoxygen sensor output based on the correction factor and the measuredoxygen (e.g., the first output). The corrected oxygen sensor output maybe the oxygen sensor measurement corrected for the part-to-partyvariability and/or change in the oxygen sensor reading over time. Thecorrected oxygen sensor reading may then be used for additional enginecontrols and estimates such as an estimate of EGR flow if the oxygensensor is an intake oxygen sensor positioned in the engine intake.

FIG. 5 shows a graph illustrating the difference in percent ethanol dueto sensor-to-sensor variation. For example, a curve 502 shows a firsttransfer function for a normal sensor. A curve 504 shows a secondtransfer function for a sensor which indicates a lower than normalpercent ethanol. A curve 506 shows a third transfer function for asensor which indicates a higher than normal percent ethanol. As shown,due to differences such as part-to-part variability, different sensorsmay indicate different values for percent ethanol in the sameenvironment. As such, the alcohol transfer function may be corrected asdescribed above based on first and second outputs of the oxygen sensorsuch that sensor-to-sensor variation is reduced and a more accurateindication of the amount of alcohol in the fuel may be identified.

Referring now to FIG. 6, a flow chart depicting a general controlroutine 600 for adjusting engine operating parameters based on an amountof alcohol (e.g., a corrected amount of alcohol determined based on thecorrected transfer function as described above) in fuel injected to theengine is shown. Specifically, one or more engine operating parametersmay be adjusted corresponding to a change in the amount of alcohol inthe fuel. For example, fuels containing different amounts of alcohol mayhave different properties such as viscosity, octane number, latententhalpy of vaporization, etc. As such, engine performance, fueleconomy, and/or emissions may be degraded if one or more appropriateoperating parameters are not adjusted.

At 610 of routine 600, engine operating conditions are determined.Engine operating conditions may include, for example, air-fuel ratio,fuel injection timing, and spark timing. For example, the ratio of airto fuel which is stoichiometric may vary for varying types (e.g., 14.7for gasoline, 9.76 for E85) and fuel injection timing and spark timingmay need to be adjusted based on the fuel type.

Once the operating conditions are determined, an updated amount ofalcohol in the fuel mixture and the ambient humidity are determined at612 of routine 600. As described above, the fuel type may be determinedbased on outputs from an exhaust gas or intake air sensor. After thefuel type is known, routine 600 proceeds to 614 where, under selectedoperating conditions such as cold start or transient fueling conditions,one or more desired operating parameters are adjusted based on theamount of alcohol in the fuel. For example, the system may adjust adesired air-fuel ratio for combustion (e.g., the stoichiometric air-fuelratio) based on the estimated amount of alcohol in the fuel. Further,feedback air-fuel ratio control gains may be adjusted based on theamount of alcohol in the fuel. Further still, the desired air-fuel ratioduring cold starting may be adjusted based on the amount of alcohol inthe fuel. Further still, spark angle (such as spark retard) and/or boostlevels may be adjusted based on the amount of alcohol in the fuel.

In some embodiments, for example, the timing and/or amount of the fuelinjection in one or more cylinders may be adjusted. For example, if itis determined that the amount of alcohol in the fuel is increased (e.g.,from 10% ethanol to 30% ethanol) during cold start conditions, theamount of fuel injected to the engine may be increased.

As another example, spark timing may be adjusted based on the detectedamount of alcohol in the fuel. For example, if the detected percentageof alcohol is lower than previously detected (e.g., from 85% ethanol to50% ethanol), the spark timing may be retarded in order to achieve ahigher engine output or boost without knock.

Thus, various engine operating parameters may be adjusted duringselected operating conditions based on a detected amount of alcohol inthe fuel injected to the cylinders of the engine. In this manner, engineand/or emissions efficiency as well as fuel economy may be maintained orimproved.

As one embodiment, a method comprises during engine non-fuelingconditions, applying each of a first, lower voltage where watermolecules are not dissociated and a second, higher voltage where watermolecules are fully dissociated to an exhaust oxygen sensor. The methodfurther comprises learning a correction factor for the sensor based on aratio of first and second outputs generated upon applying the first andsecond voltages, respectively and estimating an ethanol content of fuelcombusted in the engine by applying the learned correction factor to atransfer function based on the first output. The engine non-fuelingconditions include a deceleration fuel shut-off event, the methodfurther comprising, adjusting an engine operating parameter based on theestimated fuel ethanol content, the parameter including an air-fuelratio for combustion. The first output includes a first pumping currentgenerated responsive to applying the first, lower voltage and the secondoutput includes a second pumping current generated responsive toapplying the second, higher voltage, the first and second outputsindicative of a humid air oxygen amount, and wherein the first, lowervoltage is below a middle voltage and the second, higher voltage isabove the middle voltage, the middle voltage being a voltage where watermolecules in the air are partially dissociated, the middle voltagegenerating a third pumping current indicative of a dry air oxygenamount. In one example, the middle voltage may be 920 mV while thefirst, lower voltage is 450 mV and the second, higher voltage is 1080mV. Additionally, the exhaust gas oxygen sensor is located upstream ofan exhaust catalyst and upstream of an inlet of an EGR passageconfigured to recirculate exhaust residuals from an exhaust manifold toan intake manifold of the engine.

As another embodiment, a method comprises while purge and crankcaseventilation gases are not ingested in an engine, applying each of afirst, lower voltage where water molecules are not dissociated and asecond, higher voltage where water molecules are fully dissociated to anintake oxygen sensor. The method further comprises learning a correctionfactor for the sensor based on a ratio of first and second outputsgenerated upon applying the first and second voltages, respectively andestimating an ethanol content of fuel combusted in the engine byapplying the learned correction factor to a transfer function based onthe first output. The first output includes a first pumping currentgenerated responsive to applying the first, lower voltage, the firstoutput indicative of a humid air oxygen amount, and the second outputincludes a second pumping current generated responsive to applying thesecond, higher voltage, the second output indicative of an increase inoxygen due to dissociation of humidity, and a ratio between the firstoutput and second output is indicative of a dry air oxygen amount. Theintake oxygen sensor is located upstream of an intake throttle, anddownstream of an outlet of an EGR passage configured to recirculateexhaust residuals from an exhaust manifold to an intake manifold of theengine. The method further comprising estimating an EGR flow rate in theEGR passage based on an adjusted output of the intake oxygen sensor, theadjusted output of the intake oxygen sensor based on an output of theintake oxygen sensor and the learned correction factor.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for an engine, comprising: during selected conditions,operating an oxygen sensor at a lower reference voltage where watermolecules are not dissociated to generate a first output and at a higherreference voltage where water molecules are fully dissociated togenerate a second output; and learning a correction factor for thesensor based on the first and second outputs.
 2. The method of claim 1,further comprising adjusting a parameter based on an alcohol content,the alcohol content of fuel combusted in the engine estimated based oneach of the first output and the learned correction factor.
 3. Themethod of claim 2, wherein the parameter is a desired engine air-fuelratio for combustion.
 4. The method of claim 1, wherein the first outputincludes a first pumping current generated responsive to the operatingat the lower reference voltage and wherein the second output includes asecond pumping current generated responsive to operating at the higherreference voltage.
 5. The method of claim 1, wherein the first output isindicative of a humid air oxygen reading and the second output isindicative of an increase in oxygen due to dissociation of humid air andwherein a dry air pumping current is based on a ratio between the firstoutput and the second output, the dry air pumping current indicative ofa dry air oxygen reading.
 6. The method of claim 1, wherein thecorrection factor is a dry air correction factor that compensates forpart-to-part variability of the sensor, and wherein learning thecorrection factor based on the first and second outputs includeslearning the correction factor based on a ratio of a reference sensoroutput relative to a ratio between the first output and the secondoutput.
 7. The method of claim 6, wherein a reference alcohol transferfunction of the sensor is based on the reference sensor output.
 8. Themethod of claim 7, wherein the alcohol content of fuel estimated basedon each of the first output and the learned correction factor includes:adjusting the reference alcohol transfer function of the sensor based onthe learned correction factor; and applying the adjusted alcoholtransfer function to the first output of the sensor.
 9. The method ofclaim 1, wherein the oxygen sensor is a universal exhaust gas oxygensensor coupled to an exhaust manifold of the engine, upstream of anexhaust catalyst.
 10. The method of claim 9, wherein the selectedconditions include engine non-fueling conditions, the engine non-fuelingconditions including a deceleration fuel shut-off event.
 11. The methodof claim 1, wherein the oxygen sensor is an intake oxygen sensor coupledto an intake manifold of the engine, upstream of an intake compressor.12. The method of claim 11, wherein the selected conditions include EGRbeing enabled and no purge or crankcase ventilation gases being receivedin the intake manifold.
 13. A method, comprising: during enginenon-fueling conditions, applying each of a first, lower voltage wherewater molecules are not dissociated and a second, higher voltage wherewater molecules are fully dissociated to an exhaust oxygen sensor;learning a correction factor for the sensor based on a ratio of firstand second outputs generated upon applying the first and secondvoltages, respectively; and estimating an ethanol content of fuelcombusted in the engine by applying the learned correction factor to atransfer function based on the first output.
 14. The method of claim 13,wherein the engine non-fueling conditions include a deceleration fuelshut-off event, the method further comprising, adjusting an engineoperating parameter based on the estimated fuel ethanol content, theparameter including an air-fuel ratio for combustion.
 15. The method ofclaim 13, wherein the first output includes a first pumping currentgenerated responsive to applying the first, lower voltage and the secondoutput includes a second pumping current generated responsive toapplying the second, higher voltage, the first and second outputsindicative of a humid air oxygen amount, and wherein the first, lowervoltage is below a middle voltage and the second, higher voltage isabove the middle voltage, the middle voltage generating a third pumpingcurrent indicative of a dry air oxygen amount.
 16. The method of claim13, wherein the exhaust gas oxygen sensor is located upstream of anexhaust catalyst and upstream of an inlet of an EGR passage configuredto recirculate exhaust residuals from an exhaust manifold to an intakemanifold of the engine.
 17. A method, comprising: while purge andcrankcase ventilation gases are not ingested in an engine, applying eachof a first, lower voltage where water molecules are not dissociated anda second, higher voltage where water molecules are fully dissociated toan intake oxygen sensor; learning a correction factor for the sensorbased on a ratio of first and second outputs generated upon applying thefirst and second voltages, respectively; and estimating an ethanolcontent of fuel combusted in the engine by applying the learnedcorrection factor to a transfer function based on the first output. 18.The method of claim 17, wherein the first output includes a firstpumping current generated responsive to applying the first, lowervoltage, the first output indicative of a humid air oxygen amount, andwherein the second output includes a second pumping current generatedresponsive to applying the second, higher voltage, the second outputindicative of an increase in oxygen due to dissociation of humidity, andwherein a ratio between the first output and second output is indicativeof a dry air oxygen amount.
 19. The method of claim 17, wherein theintake oxygen sensor is located upstream of an intake throttle, anddownstream of an outlet of an EGR passage configured to recirculateexhaust residuals from an exhaust manifold to an intake manifold of theengine.
 20. The method of claim 19, further comprising estimating an EGRflow rate in the EGR passage based on an adjusted output of the intakeoxygen sensor, the adjusted output of the intake oxygen sensor based onan output of the intake oxygen sensor and the learned correction factor.